The present invention relates to a device for treating blood by extracorporeal circulation, a disposable line for use in a circuit for extracorporeal circulation of blood having undergone pre-infusion of anticoagulant, and a method for anticoagulation of the blood treated by extracorporeal circulation.
A haemodialysis session requires anticoagulation of the blood circulating in the extracorporeal circulation line in order to avoid coagulation of the blood in contact with the synthetic materials (circulation lines, dialyser fibres). This anticoagulation is most often performed using heparin, which is known for its anticoagulant properties. Heparin is injected as pre-infusion into the arterial line of the device, and it is then present in the entire extracorporeal circuit of the blood, from pre-infusion until re-injection of the blood into the patient. Consequently, upon return of the blood, the patient is administered doses of heparin. Although it is necessary to prevent coagulation in the extracorporeal circulation line, in some cases the risk of the patient bleeding may pose a danger. This is particularly true of patients at high risk of haemorrhaging (for example in the days following major surgery) or in those patients with hypersensitivity to heparin. Consequently, anti-coagulation with heparin may prove dangerous to the patient on account of heparin being injected via the return of blood to the patient.
FIG. 1 shows a device for treating blood by extracorporeal circulation 1 according to the prior art, comprising a filter 2 having a first chamber 3 and a second chamber 4 separated by a semi-permeable membrane 5. The device comprises an arterial line 6 connected to the first chamber 3 of the filter for the circulation of blood taken from a patient 7, and a venous line 8 issuing from the first chamber of the filter. A pre-infusion channel 9 is connected to a container 10 comprising a solution of heparin and is linked to the arterial line 6, the function of the solution being to prevent coagulation of the blood outside the patient's body, and a purge channel 11 issuing from the second chamber 4 of the filter. An air separator 12 is linked to the venous line 8. The air separator 12 also comprises an air detector 13, and a clamp 14 is placed on the venous line 8 downstream of the air separator 12, that is to say downstream in the direction of circulation of the blood in the venous line 8. The clamp allows the flow of blood to be arrested in the event of air bubbles being detected by the detector 13 before the blood returns to the patient 7.
Thus, as was mentioned above, the solution of heparin acts against coagulation of the blood throughout the device 1 and also in the patient's body. Consequently, the return and injection of heparin into the body of the patient 7 can prove dangerous.
Patent application PCT/EP00/03583 concerns an infusion fluid of substitution, in particular for use in haemofiltration of blood, and an anticoagulant solution with citrate for regional anticoagulation. In order to avoid coagulation of blood during a haemodialysis session, it is known that citrate ions can be used as anticoagulant. The citrate ions, added to the blood in the extracorporeal circuit before they enter the artificial kidney, are active as anticoagulants. Thus, the risk of complications with bleeding due to systematic anticoagulation is avoided. During the haemofiltration, some of the citrate ions pass through the artificial kidney. The citrate ions are active as anticoagulants only in the extracorporeal circuit because, when they reach the systemic circulation of the patient, they are rapidly metabolized to bicarbonate ions. The subject of patent application PCT/EP00/03583 is a solution of a certain composition.
FIG. 2 shows a device for treating blood by extracorporeal circulation 1 described in patent application PCT/EP00/03583. This device 1 comprises a filter 2 having a first chamber 3 and a second chamber 4 separated by a semi-permeable membrane 5. The device comprises an arterial line 6 connected to the first chamber 3 of the filter for the circulation of blood taken from a patient 7, and a venous line 8 issuing from the first chamber of the filter. A pre-infusion channel 9 containing an anticoagulant, trisodium citrate, is connected to a container 10 comprising a solution of citrate ions and is linked to the arterial line 6, the function of the solution being to prevent coagulation of the blood outside the patient's body. A purge channel 11 is linked to the outlet of the second chamber 4 of the filter, and an air separator 12 is linked on the venous line 8.
The venous line 8 comprises, in addition to the bubble trap 12, a channel 13 connected to a container 14 comprising a solution for re-establishing the ionic equilibrium of the blood. The citrate solution renders the blood anticoagulable by decalcifying it upstream of the filter. This channel 13 is linked downstream of the bubble trap 12, that is to say downstream in the direction of circulation of the blood in the venous line 8 before the blood is returned to the patient 7.
The reason is that, in order to re-establish correct haemostasis, the ionic equilibrium of the blood must be re-established, specifically by recalcifying it, after leaving the filter.
The teaching of this document comprises a safety device with which it is possible to detect any air bubbles present at the start of the venous line. By contrast, the device described does not have any safety means for detecting and trapping any air bubbles in the post-infusion line linked to the venous line, and return of air to the systemic circulation of the patient, which is very dangerous for said patient, is possible.
In seeking to solve this problem, the persons skilled in the art have tried linking the post-infusion line, containing an infusion solution of substitution, directly to the bubble trap of the venous line and not downstream thereof. Moreover, the bubble detector has been placed on this bubble trap. In this way, a single device makes it possible simultaneously to separate and detect the air bubbles coming from, on the one hand, the blood liquid extracted from the filter and, on the other hand, coming from the post-infusion liquid.
However, in trials carried out with this set-up, it has been found, especially in prolonged operation, for example with slow blood flowrates in an intensive care unit, that although the problem of air bubbles in the two liquids is solved, a new problem arises: namely that of coagulation within the bubble trap. This is because the blood liquid extracted from the filter and arriving in the bubble trap comprises an anticoagulant liquid which has been injected in pre-infusion into the patient's blood during its passage through the arterial line. Moreover, the bubble trap also receives an infusion solution of substitution, whose effect is to neutralize the anticoagulant effect of the pre-infusion solution. The structure of the bubble trap is such that on the one hand the liquid passing inside the latter is in contact with the air and the risk of coagulation is present, and, on the other hand, as the bubble trap has a greater diameter than the diameter of the venous line, the flowrate of liquid is thereby diminished and the phenomenon of coagulation thereby promoted.
It is also known in U.S. Pat. No. 5,330,425 (Utterberg) a device concerning the injection in the venous line of drugs and the like. It is also known an haemodialysis machine having an air-detector/line clamp assembly mounted on the venous line typically at least two inches below a venous chamber, in which it is possible to design a venous bloodline wherein an injection site is placed in the tubing downstream of the venous chamber, yet upstream of the air-detector/line clamp.